At 05:28 AM 4/29/2008, you wrote:
>I have conflicting information on this subject, if twisted pair is best
>how mant twistes, the norm seams to be one per winding.
This is an area where a lot of folklore prevails.
You are basically trying to build a transmission line, it can work as
two wires together parallel to each other, but it's hard to keep them
that way so people twist them which insures the wires are
consistently close to one another. How much twist? There are lots of
opinions but if you don't twist them enough you can get to the point
where the wires are not consistently at the same distance to one
another. A good example is how commercial outfits do it in CAT5
cable, they do about 2 to 3 twist to the inch, CAT5 cable is designed
to be a transmission line.
Why a transmission line? You often see people recommend that it does
not make a difference, they are wrong it makes a huge difference but
maybe one they either don't care about or are ignorant about it.
A conventional transformer specially at RF is subject to many
problems, the core saturating, nonlinearities in the core's
inductance, capacitive coupling between the windings (leakage) that
make it inefficient and subject to poor frequency response, the power
is coupled from the primary to the secondary by a magnetic field in
the core so the coupling is affected by the core properties.
In order to minimize those problems there is a different way to make
a transformer, although it seems similar it works on quite a
different principle. The transformer is know as a Transmission Line
Transformer or TLT for short it does not use a magnetic field through
the core to transmit the power from the primary to the secondary. The
core is there for a totally different purpose. The windings transfer
power through Transverse Electro-Magnetic (TEM for short) fields in
the transmission lines, the core's purpose is to reject common mode
signals wanting to flow back through the windings. Because the core
is not transmitting the power the response of the transformer is very
flat across a huge segment of frequencies, I bought some TLT
transformers in a previous buy that had a flat response from 50KHz to
300MHz and cost about a dollar. I have a set of isolating
transformers that I bought for the softRocks that are flat from 5Hz
to 300KHz and that was only possible because it was built as a TLT
transformer, unfortunately they are not made any more. I wish I had
bought several sets.
"Blessed are the cracked, for they shall let in the light."